Multiplex carrier-wave transmission



Nov. 24, 1925- 1,562,964

A J. w. HORTON MULTIPLEX CARRIER WAVRTRANSMISSION Filed Feb, 28, 1923 Joseph WHW/0x7 by A//y Patented Nov. 24, 1925.

UNITED STATES PATENT OFFICE..

JOSEPH W. HORTON, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMRANY, INCORPORATED, OF NEW YORK. N. Y., A CORPORATION OF NEW YORK.

MULTIPLEX CARRIER-WAVE TRANSMISSION.

Application filed February 28, 1923. Serial No. .621,736t

To all whom t may concern.'

Be it known that I, J osnPH W. HoR'roN, a citizen of the United States of America, residing at Bloomfield, in the county of Essex 5 and State of New Jersey, have invented certain new and useful Improvements in Multiplex Carrier-'Wave Transmissions, of which the following is a full,` clear, concise, and

exact description. y

rIhe present invention relates to signaling by means of sustained waves commonly known in the art as carrier waves, which may be either radiated through space or transmitted over a transmission line.

The invention relates moreparticularly `to a type of carrier wave transmission in which auxiliary or reinforcing waves, definitely related in frequency to the received waves, are used at a receiving point, for the purpose of assisting in the reception of the signals.

A system of the type to which the invention is applicable is described in a paper by Colpitts and Blackwell entitled Carrier current telephony and telegraphy, appear- 5 ing in a series of instalments in the Journal of the American Institute of Electrical Engineers beginning April '1921, the particular type of system referred to being illustrated in Fig. 49 of that paper.

In the system disclosed inthe figure to which reference has been made, the auxiliary or reinforcing waves employed at the receiving point are derived as harmonics of a wave of base frequency which may be transmitted from the sending station along with the carrier waves. In the particular system there disclosed the auxiliary or reinforcing waves have frequencies identical with those of the respective carrier waves.

'40 The carrier waves sent from the transmitting station are derived from a wave of the same base frequency as that transmitted to the receiving station, and it is therefore only necessary to select the corresponding harmonies of this base frequency wave at the respective stations to provide waves of respectively the same frequency.y

Under some conditions of operation. it becomes inconvenient or undesirable to transmit a wave of relatively low base frequency through the system in order to provide the auxiliary or reinforcing waves at the receiving point. In a system employing carrier waves which are derived as harmonics of a base frequency, the frequency of the base or "fundamental wave is determined by the frequency spacing which the carrier waves are to have. For example, if

only a ysingle side band is transmitted through each carrier channel, as is now common practice, considerations of economy in total frequency range make it desirable to space the carrier waves the order of 3000 to 5000 cycles apart. This necessitates the use of a base or fundamental frequency of the order of 3000 to 5000 cycles although the lowest carrier frequency of the system may be of the order of 10,000 or 15,000 cycles. Ifthe frequency range below the lowermost carrier channel is to be employed for other purposes such as ordinary speech transmission, wave telegraphy, or the like, it frequently encumbers the system to have to reserve in this lower frequency range a channel for the base frequency wave to be used for deriving the telephone carriers. Also as respects the terminations for the various kinds of signaling carried on over the line, the use of mid-line repeaters, the interconnection of'different lines, etc., it often proves very inconvenient to tie up the carrier telephone channels with the circuitsor channels which employ the lower frequency range and which are used for other purposes.

The invention provides for the production of auxiliary or reinforcing waves at a receiving point, bearing a definite relationto the frequency of t-he received waves, without the necessity. of transmitting through the system any wave having a frequency lower than the frequencies actually employed by the carrier channels themselves.

The specific manner of producing and con:

trolling the auxiliary or reinforcing waves at a receiving point according to the invention comprises the transmission of two waves differing in frequency by the same interval as two neighboring carrier channels. These two waves are caused to interact at the receiving point to produce a wave of a frequency equal. to the difference between the frequencies of the two waves, and this wave of the difference lfrequency is used as a fundamental or base from which a series of harmonic waves are generated. At the transmitting point the carrier waves and also the two waves used for frequency control are derived as harmonics of a base or fundamental wave which likewise has a frequency equal'to the frequency interval between the quencies, and these` may be as high las or l higher` than the carrier waves.

type disclosed tion, both as to its construction and of operation,

y to: the invention.

` connected bythe main line i ,ordinary telephone-lines Ll loop A more detailed description of the inven-` tion as applied to a system of the general y Iin the above mentioned Fig. 49 of the `Colpitts and Blackwell publicamanner will now be given, with `particular reference tothe accompanyin draw? ing Whichshowsin sc'hematic form t epre-` ferred arrangement of aV system according The drawing shows a two-Way carrier telephone system comprising terminal stations Incoming to the West station of the system are the and L2 which cooperate in the two-Way `transmission of signals with the respective telephone lines 3 and L ,c terminating yin the east station. Each of the lines `is provided with a balanc\ i ing network N1 etc. and a differential repeating coil in accordance with standard telephone repeater practice for enabling cur` `rents to be applied to the respective line and erived therefrom without mutual interference. Each of the lines at each station is connected through a carrier Wave transmitting branch to a common transmitting loop TL and similarly through a carrier receiving branch to a common receiving loop RL. The carrier Waves that are used for transmission from West to east through the system are assumed to have respective frequencies which, as a group, are higher than the frequencies employed for transmission in the opposite direction. The west to east transmissions may therefore be separated as a group from the oppositclv directed transmissions by means of the high pass filters HP, which transmit only the high group,

p and the low pass filters LP, which transmit only the lower group. The transmitting TL ofthe West station is connected to the line ML through the filterHP of the station, and the receiving loopRL of the east station is connected to the line ML through the filter HP of that station. Similarly the filter LP of the West station connects-the receiving loop RL of, that station with the line ML, and the filter' LP of the east station connects the transmitting loop TL of that station with the line ML.

The filters HP and LP, and each of the other filters of the system to be referred to, may be constructed and designed in accordance with the disclosure in the above mentioned Golpitts` and Blackwell publication and also in accordance with the disclosure to the line ML.

of the patent to G. A. Campbell, No. 1,227,- 113, May 22,1917. As described in the above mentioned article, the term high pass 'filter is used denote a 'filter having substantially uniform negligible attenuation for i currents of all frequencies higher than a predeter- `mined cut-olf frequency and substantially infinite attenuation for currents of frequencies lower'than this'cut-off frequency. Converselya low `pass filter is one which freely transmits currents ofall frequencies below a limiting frequency and effectively suppresses transmissionof all currents of higher frequency. y j i The currents of the various carrier Waves employed by the west station in transmitting and `receiving are .derived as harmonics from a `Wave of base frequency supplied from the source S, these waves being applied to a harmonic generatorl HG., which produces a "series of harmonic frequency Waves under control of the applied Wave. These harmonicspass into the harmonic supply path HS1 `from which they are selected for the individual use of the channels by the selective circuits F1, F2 and F5, F3. These selective circuits may be simple tuned circuits or filters ofthe type shown in the Campbell patent, and have preferably a relatively narrow transmission band. Each carrier transmission branch containsa modulator such as M1 and a band filter BF1 and each carrier receiving branch contains a band filter suchy as BF5 anda detector or cle-modulator D.. The modulators are preferably of the balanced type for suppressing transmission of the unmodulated carrier Wave component. The carrier Waveto be used by the uppermost channel of the West Station is selected from the harmonic supply circuit HS1 by a 105 selective circuit F1 and is vapplied to the modulator 1 ,in the manner disclosed in Fig. 49 of thelolpitts and Blackwell article cited. The modulated carrier Wave result- 1 ing from the interaction of this carrier with speech received over the line L1 is applied to the channel band filter BF1 which preferably suppresses transmission 'of one of the two side bands and permits transmission of the other. The selective circuit Fg, modulator M2, and the band filter BF2 similarly cooperate with the line L2 to` apply to the transmitting loop TL a speech side band of the carrier Wave of the frequency employed by that channel. Any desired number of modulated carrier Waves of respectively different frequency may similarly be applied to the transmitting loop TL from which they pass selectively through the filter HP The filter BF5 is designed to select from the frequencies in the receiving loop RL received over the line ML from the distant station. the particular speech side band which iste be' used in repeating-speech into 130 the line L1. This side band after selection is applied to the detector or demodulator D1 in the manner indicated in Fig. 49 of the Colpitts and Blackwell publication. There is simultaneously applied to this detector from the branch HS by means of the selective circuit F5, a reinforcing wave of the same frequency as the carrier wave used by this channel at its transmitting terminal at the East station. The demodulated speech is transmitted from the output of the detector l)1 to the line L1. In similar manner the band filter BFG, the detector D2, and the tuned circuit Fb. cooperate to repeat into the line L2 the speech transmitted over a second carrier channel, and other similar receiving channels may be provided as desired.

The arrangement of the east station as respects the lines L3 and L4 and the carrier transmitting andreceiving branches may be entirely similar to those described of the west station, and the various notations used on the figure will malte clear the identity of the various element'sfand their manner of i cooperation. It will be understood that the channel band filters serving respectively for transmitting and receiving the same wave at the two stations will have the same transmission frequency band. For example filters BF1 and BF7 have the same transmission range; also filters BF, and BF5 have identical ranges; and so with each pair in the 'same channel.

.Between each detector and the low frequency line into which it'repeats there may be inserted, if desired, a filter LF such as is shown in connection with the line L3 for selectively transmitting currents of speech range but suppressing transmission of currents of higher frequency.

The construction and operation of each of the elements such as the. source S, the harmonic generator HGrn and the band filters, are disclosed in the Colpitts and Blackwell publication. For fflrther reference as to the preferred construction of these, elements the patent to Hartley 1,356,763, October 26` 192() may be consulted as ltothe source S; the British Patent142,'571 may be consulted as to the harmonic generator; the patent to Carson 1,343,306, J une 15, 1920, `may be consulted as to the modulators` and demodulators, and the patent to Campbell above referredto may be consulted on the band filters.

In addition to the waves employed by the several channels for transmitting speech between the terminal stations in the manner that has been described, the invention p rovides fortransmitting from one of the stations', say the west station, two waves which are used for frequency control. These waves may have any desired frequency, but according to the invention they differ in frequency by the same amount as two adjacent carrier waves used by the system. The frequency control waves are derived from the harmonic generator HGro by the band filter BF0 which is` designed to have a transmission range of the proper breadth to include the two frequency control waves. For eX- ample, the filter BF, may selectively pass the two successive harmonics next higher than the carrier wave of highest frequency used,

by' the signaling channels of the system. However, the frequency control waves may have any other desired absolute frequency values so long as they differ from, each other by the proper frequency interval. Since the frequency control waves lie in the frequency range transmitted from the west station, they will pass through the filter HP of this station over theline ML and through the filter HP of the east station into the receiving loop RL, from which they areselected bythe band filter BFl having atransmission range equivalent to that of the filter BFO. The two Waves thus selected are applied to the detector D0, which may be a simple detector of the audion type having a nonlinear relation between applied voltage and output current. Such a detector has the property of producing in its output circuit a wave having a frequency equal to the difference in frequency of the impressed waves, and in the present case this wave will therefore have a frequency equal to the frequency interval between respective carriers. This base or fundamental wave is selectively transmitted through the low pass filter LFO, which is designed to suppress transmission of components of higher frequency, and is applied, to the circuit of the harmonic generator HG, which may be similar or identical tothe harmonic generator HGO. The circuit from this point on may be identical in construction and operation with the output circuit of the harmonic generator HGO. the harmonics developed at HGr being 4applied to the harmonic supply circuit HS2. `As in the case of thewest station, the harmonic selected to each modulator is of the frequency to be used as the carrier for that particular channel, and the harmonic which is selected as the reinforcing Wave to be applied to each detector is of the same frequency as the car rier wave of that receiving channel.

The circuits and system that have been illustrated and described in .detail should be considered as merely typifying what is at present deemed the preferred form of practicing the invention, but are not to be construed as limiting the nvention, its scope being defined in the claims.

What is claimed is: y

1. In a carrier wave transmission system, a sending station and a receiving stationa source of base frequency waves at the sending station, a harmonic generator associated with said source to produce a plurality v l n a a sending station and a receiving station, a

-source of base frequency waves at the sending station, a harmonic generator associated with said source to produce a plurality .of

harmonic frequency waves,A- circuits for selecting and controlling certain of said harmonic frequency waves in accordance with signals to be transmitted, a circuit associ' ated with said harmonic generator for transmitting two other harmonic frequency waves, circuitsat the receivingstation to receive the signal vcontrolled waves, a circuit to receive the other two waves, means to derive from the interaction of said two waves a wave of base'frequency and to produce harmonicfrequency waves therefrom,

and means for utilizing the harmonic frequency waves so produced in reproducing the transmittedsignals.

.i 3. In a carrier wave transmission system, a transmission line, 'a source of base frequency waves, a harmonic generator adapted to produce a plurality of harmonic frequency waves and having an input circuit associated with said source and an output circuit associated with said line, circuits associated withsaid output circuit for selecting and controlling certain of said harmonic frequency waves in accordance with'si-gnals to be transmitted, means in said output cir'- cuit for selectively transmitting a plurality of other harmonic frequency waves to said line, circuits for selectively receiving the Signal controlled waves transmitted over said line, a circuit to receive the other harmonic frequency waves transmitted over said line, means to derive from the last mentioned waves a wave of the base frequency, means to reproduce harmonic frequencyv waves from said last mentioned base frequency wave, and means for combining the harmonic frequency waves so produced with the signal controlled waves to reproducel the transmitted si als.

4. In a carrier wave transmission system, a transmission line, va plurality of trans-` mitting channels associated with said line, a source of base fre uency waves, a-harmonic generator associated with said source to produce a plurality 0f harmonic frequency waves, circuits for selectively transmitting said harmonic frequency waves to said channels, means associated v with said channels to control the h armonic frequency waves in accordance with signals to be trans-y mitted and for selectively transmitting the waves so controlled to said line, a circuit associated with said harmonic frequency generator for selectively transmitting other harmonic frequency waves to said line, circuits for receiving the controlled waves transmitted over said line, a circuit for receiving the other harmonic frequency waves transmitted over said line, means associated with said last mentioned circuit to derive from said last mentioned waves a wave of the base frequency, a harmonic generator for producing harmonic frequency waves from the derived base frequency wave, and means for combining the harmonic frequency waves so produced with the received signal controlled waves to reproduce the transmitted signals. 5. In a carrier wave transmission system, a sending station and a receiving station interconnected by a transmission line, a plurality of two-way channels associa-ted with the line at each of said stations, a source of base frequency waves at said sending station, a har'- monic generator associated with said source toA produce a plurality 'of harmonic frequency waves, circuits for selectively transmittingl the harmonic )frequency waves to said channels, means associated withi said channels for modul-ating the harmonic frequency waves in accordance signalV vwaves therein, means associated with each of said channels for selectively transmitting certain of said `modulated waves to said line, a circuit associated with said harmonic frequency generator for selectively transmit-v ting two other harmonic frequency waves to sai-d line, circuits' at said receiving station for selectively receiving the modulated waves transmitted over said4 line, a circuit for receiving said two harmonic frequency waves transmitted over said line, a detector associated with said last mentioned circuit to derive from said last mentioned waves a wave of the base frequency, a harmonic generator for producing harmomc frequency waves from the derived base frequency wave,

modulating circuits associated with the twoway channels at said receivingstation, and circuits vfor selectively impressing the `derived harmonic frequency waves and the received modulated waves upon said modulating circuits to reproduce the transmitted signals. f

, 6.aIn a carrier signaling system, means to produce a plurality of carrier waves having the same fundamental lfrequency separation, means to modulate eachof said carrier waves by speech and to suppress the transmission ofthe unmodulated carrier component of each carrier, means to produce two other Magee@ y waves ofthe same fundamental frequency separation as said carrier waves, said two waves having frequencies at least as high as the lowest frequency of the carrier waves, means t0 transmit all of said waves to a distance, means to Iderive from said two waves a wave of said fundamental frequency, means to derive from the fundamental frequency wave so derived a plurality of waves l@ identical in frequency with the respective,

respective received waves to reproduce the,

speech transmitted by each of said. carrie-r waves.

In witness whereof, I hereunto suhscriloe my name this 16 day ofFebruaryA. D., 1923. 'e

JosErHW. Honrou. 

